The overall goal of this project is to gain greater understanding of adult hippocampal neurogenesis, its mechanisms and regulation. Adult neurogenesis has important implications for designing strategies of neural replacement therapy, which could be used to treat neurodegenerative disorders and other conditions of neuronal loss. Previous studies have indicated that the adult hippocampus contains multipotent progenitors, which are the ultimate source of new neurons. However, the multipotent progenitors do not produce new neurons directly, but instead produce distinct "intermediate progenitors", which divide further to generate new neurons. The properties and dynamics of intermediate progenitors are poorly understood, due in part to a lack of specific markers. Preliminary studies for this proposal suggest that Tbr2/Eomes (hereafter referred to simply as Tbr2), a T-domain transcription factor, is specifically expressed in the intermediate progenitors. Aim 1 of this proposal is to define the cellular, molecular, and lineage properties of Tbr2+ cells, and confirm whether they correspond to intermediate progenitors. Aim 2 is to correlate changes in the number of Tbr2+ cells with regulation of neurogenesis induced by running wheel exercise and antimitotic drug treatment. Aim 3 is to define mechanisms of adult neurogenesis regulated by Tbr2 by studying mice with conditional gene inactivation. Aim 4 is to characterize the dynamics of intermediate progenitor cell division, migration, and differentiation by time-lapse imaging of hippocampal slices from normal mice, and from mice with Tbr2 inactivation. By shedding new light on the role and properties of intermediate progenitors and new neurons, this project may potentially lead to breakthroughs in adult neurogenesis and neural replacement therapy. PUBLIC HEALTH REVELANCE: Recent advances in neural stem/progenitor cell biology have raised the possibility that neurodegenerative diseases and other conditions of neuronal loss, such as trauma and stroke, could be treated by neural replacement therapy. This project will study adult hippocampal intermediate progenitor cells, a special type of neural progenitors that produce glutamatergic neurons, similar to those that are depleted in Alzheimer dementia and other diseases that affect the cerebral cortex.